Bass tone producing device for an electronic musical instrument

ABSTRACT

In a keyboard electronic musical instrument having pedal keys, a bass tone producing device comprises a fundamental bass tone signal source for generating 16&#39;&#39; bass tone signals having predetermined pitches for the respective pedal keys, and two harmonic bass tone signal sources for respectively generating 8&#39;&#39; and 4&#39;&#39; bass tone signals. Output signals from the three bass tone signal sources are respectively supplied to three keyer circuits which are gang operated by a pedal key to be rendered conductive upon depression thereof. On the one hand, the three different bass tone signals obtained through the keyer circuits are mixed in a predetermined ratio and supplied to a tone coloring filter having a peak frequency of about 100 to 300 Hz to establish a first composite signal. On the other hand, the two harmonic bass tone signals are mixed in a predetermined ratio, passed through a phase inverter, and applied to another tone coloring filter having a peak frequency of about 1,000 Hz to establish a second composite signal. Both of the composite signals are finally mixed to form desired bass tones having clear harmonic components.

' United States Patent 91 Adachi 1451 Mar. 27, 1973 [54] BASS TONEPRODUCING DEVICE FOR 3,610,804 10 1971 Matsuura ..84/l.l7

AN ELECTRONIC MUSICAL 3,694,561 9 1972 Morez INSTRUMENT 3,697,66410/1972 Hiyama ..84/ 1.17

[75 Inventor: Takeshi Adachi, Hamamatsu, Japan primary Rj a WilkinsonAssignee: J-

Kaisha Hamammswsm, Japan Attorney-Robert D. Flynn et al.

[22] Filed: June 13, 1972 [57] ABSTRACT [21] Appl. No.: 262,229 In akeyboard electronic musical instrument having pedal keys, a bass toneproducing device comprises a I fundamental bass tone signal source forgenerating 16' [30] Fmlgn Applicatmn Pnomy Data has tone signals havingpredetermined pitches for the June 16, 1971 Japan ..46/43111 respectivepedal keys, and two harmonic bass tone June 16,1971 Japan ..46/43112signal sources for respectively generating 8' and 4 bass tone signals.Output signals from the three bass [52] US. Cl. ..84/1.01, 84/ 1.17, 84/1.2, tone signal sources are respectively supplied to three a 84/ 1.23,84/ 1.26 keyer circuits which are gang operated by a pedal key [51] Int.Cl. ..Gl0h 1/06, GlOh 5/12 t be ndered Conductive upon depressionthereof. [58] Field of Search ..84/1.01, 1.111.13, 0n the one hand, thethree different a s tone g a s 84/117, 1 19 1 23,1 26,DIG, 9 obtainedthrough the keyer circuits are mixed in a predetermined ratio andsupplied to a tone coloring [56] References Cit d filter having a peakfrequency of about 100 to 300 Hz to establish a first composite signal.On the other UNITED STATES PATENTS hand, the two harmonic bass tonesignals are mixed in 1,964,522 6/1934 a predetermined ratio, passedthrough a phase in- 2,148,478 2/1939 verter, and applied to another tonecoloring filter hav- 2233948 3/1941 7 ing a peak frequency of about1,000 Hz to establish a 2,624,041 12/1952 second composite signal. 12,835,814 5/ 1958 Both of the composite signals are finally mixed to3,150,228 9/1964 form desired bass tones having clear harmonic com-3,535,969 10/1970 ponents 3,571,481 3/1971 Adachi ..84/1.13

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T2 VARIABLE RELEASED PEDAL KEY DEPRESSED FIG. 4

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SHEET 7 BF 7 1 v a P D E155 -530 D5 3- 10 F (i J- gg FREQUENCY (H BASSTONE PRODUCING DEVICE FOR AN ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OFTHE INVENTION This invention relates to a bass tone producing device foruse in an electronic musical instrument and more particularly to a basstone producing device in which a bass tone is composed of a fundamentalsignal and harmonic signal.

As is well known, the bass tones of a musical instrument are played bythe pedal keys to beat the rhythm of the music and to support melody andchord tones which are played by manual keys. A keyboard electronicmusical instrument such as an electronic organ is so designed as toproduce desired base tones upon its pedal key depression. The bass toneconsists of a fundamental tone and harmonic tones mixed in a properratio. Bass tones thus composed can have an excellent sound effect wherethe performance is given in a relatively limited room, but have adrawback where the performance is given in an appreciably spacious hall,the bass. tones presenting a muffled sensation rich in lower componentsdue to the acoustic character of the hall that the lower components havelonger reverberating time.

It is accordingly the object of this invention to provide a bass toneproducing device for an electronic musical instrument capable ofproducing bass tones having a tone color like that of a tuba, forexample, sounding clear even in a relatively large spacious hall.

SUMMARY OF THE INVENTION The bass tone producing device of thisinvention delivers, upon depression of a pedal key of an electronicmusical instrument, an ordinary bass tone signal consisting of afundamental bass tone having a prescribed pitch and harmonic signalshaving pitches of a higher octave than that of the fundamental base tonemixed in a proper ratio as well as an additional bass tone signalconsisting of the harmonics. The former bass tone signal is conductedthrough a first tone coloring filter having a relatively low peakfrequency, while the latter bass tone signal is passed through a secondtone coloring filter having a peak frequency higher than the first tonecoloring filter. The filtered two bass tone signals are blended in aproper ratio with the phase of the latter reversed or suitably shiftedso as to produce final desired bass tone signals, which are composed ingood condition free from mutual complicated interference among thecomponent signals. Tones reproduced by these composite bass tone signalshave peak tone pressures (formants) in not only a relatively lowfrequency region but also a higher frequency region, so that where anelectronic musical instrument is played in a spacious hall, the tonesdisplay an excellent rhythmical effect without presenting a muffledsensation rich in low pitch components as is often the case with theprior art bass tone producing device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block circuitdiagram'of a bass tone producing device for a keyboard electronicmusical instrument according to an embodiment of this invention;

FIG. 2 is a concrete circuit arrangement of the bass tone producingdevice of FIG. 1;

FIG. 3 is a curve diagram showing the rising and decayingcharacteristics of output bass tones from the device of FIG. 2;

FIG. 4 is a chart showing curves of the frequency characteristics of therespective filters included in the device of FIG. 2 and a curve of theactually measured frequency characteristics of composed bass tonesignals;

FIG. 5 is a schematic block circuit diagram of a bass tone producingdevice according to another embodiment of the invention;

FIG. 6 is a concrete circuit arrangement of the device of FIG. 5;

FIG. 7 is a curve diagram showing the rising and decayingcharacteristics of two types of bass tone signals delivered from thedifferent groups of keyer circuits of FIG. 6;

FIGS. 8A to SE show actually measured frequency spectra of final outputsignals produced from the circuitry of FIG. 6 at different times in itsdecay; and

FIG. 9 indicates curves of the frequency characteristics of the filtersand the mixed output in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A bass tone producing deviceaccording to the preferred embodiments of this invention will now bedescribed by reference to the appended drawings.

FIG. 1 is a schematic block circuit diagram of a bass tone producingdevice according to an embodiment of the invention. There are provided,for each one of the keys (actually 13 or 25 or 32 keys are arranged inthe order of musical notes, though only one of them is indicated), a 16'tone signal source 12 as a fundamental bass tone signal source, 8 and 4'tone signal sources 13 and 14 as harmonic bass tone signal sources. Thesource 12 is generally so designed as to generate a tone signal whosepitch is one octave lower than the notation notes in a musical staff,and is known as a 16-foot tone signal. Likewise, the harmonic bass tonesignal sources generate an 8-foot tone signal and a 4-foot tone signal,respectively.

Output signals from the 16' tone signal source 12 and the 8' and 4' tonesignal sources 13 and 14 are conducted via respective keyer circuits 15,16 and 17 gangactuated with the depression of the corresponding pedalkey 11, and individual resistors R,, R and R connected to the outputterminals of the keyer circuits 15 to 17 to be mixed in a predeterminedratio. The bass tone signals thus mixed are supplied to a tone coloringfilter 18 having a relatively low peak frequency to form a firstcomposite signal. On the other hand, output signals from the 8' and 4'tone signal sources 13 and 14 are passed through the corresponding keyercircuits 16 and 17 and separate resistors R and R connected to theoutput terminals of the keyer circuits 16 and 17 to be mixed in apredetermined ratio and, after the phase is reversed by a phase inverter19, are supplied to another-tone coloring filter 20 having a higher peakfrequency than the tone coloring filter 18 to form a second compositesignal. The above-mentioned two composite signals delivered from bothtone coloring filters l8 and 20 are introduced via individual resistors6 and 7 to be blended finally in a predetermined ratio. The bass tonesignal thus blended is properly amplified by an amplifier 21 to be fedto the next stage (not shown) in the instrument.

FIG. 2 is a concrete circuit arrangement of the bass tone producingdevice of FIG. 1. The fundamental bass tone signal source 12, and theharmonic bass tone signal sources 13 and 14 are constituted by afrequency divider chain 31 consisting of three cascade connectedbistable multivibrators 121, 131 and 141 respectively including twotransistors as TR,-TR,, TR,TR and TR -TR,.

It will be noted that the tone signal sources (generally provided in anumber of 85 or 97 corresponding to musical notes of C, to C, or C, toC,) are formed of 12 master oscillators representing one octave of thehighest musical scale and a plurality of frequency dividers cascadeconnected to the respective oscillators in turn. Accordingly, the firststage bistable multivibrator 141 constituting the 4' tone signal source14 included in the frequency divider chain 31 has its input terminal 32impressed with an output signal from a preceding frequency divider stage(not shown).

The keyer circuits 15 to 17 are constructed of emitter follower keyercircuits 151, 161 and 171 including transistors TR-,, TR, and TR,respectively whose bases are connected via forwardly directed diodes D,,D, and D, to the collectors of the corresponding transistors of thebistable multivibrators 121, 131 and 141, for example, the right sidetransistors TR,, TR, and TR, respectively. The aforesaid transistorsTR-,, TR, and TR, have their collectors directly connected to a groundedpositive source line 33, and their emitters connected via resistors R,,,R,, and R, to a line 36 which is connected to a negative source line 35via a resistor R,, and a normally open key switch 34 closed upondepression of the pedal keys 11. Between the line 36 and the negativesource line 35 is connected a capacitor C,. Between the line 36 and thepositive source line 33 is connected in parallel a resistor R and aseries circuit consisting of a resistor R,, and a variable resistor VR,having a movable contact 37 connected to the positive source line 33.

The emitters of the transistors TR-,, TR, and TR, are respectivelyconnected via the resistors R,, R and R, of the indicated values and acapacitor C, to the base of a transistor TR,, included in an emitterfollower amplifier 39 provided if required.

The tone coloring filter 18 is comprised of a low pass filter 181including an inductor L, and a capacitor C connected between one end ofthe inductor L, and the positive source line 33. The inductor L, has theother end connected via a coupling capacitor C, to the emitter of thetransistor TR,,.

The emitters of the transistors TR, and TR, are also connected to thebase of a transistor TR,, included in a grounded-emitter amplifier 191constituting the inverter 19 via the resistors R, and R, of theindicated values as well as via a coupling capacitor C, connected to thecommon connection 38 of the resistors R, and R,.

The tone coloring filter 20 is formed of a band pass filter 201including a group of an inductor L, and a capacitor C, and another groupof an inductor L, and a capacitor C,, the two groups being connected inparallel between the positive source line 33 and the collector of thetransistor TR via a coupling capacitor C, and a resistor R The amplifier21 is formed of an emitter follower amplifier 211 including a transistorTR having its base applied through a coupling capacitor C,

with the aforesaid two mixtures of bass tone signals delivered from thelow pass filter 181 and the band pass filter 201 after the mixtures arefurther blended together through the resistors R, and R of the indicatedvalues.

The operation of a bass tone producing device according to thisinvention will now be described by reference to FIG. 2. While any of thepedal keys 1] is not depressed, the corresponding key switch 34 remainsopen, the capacitor C, is charged with source voltage through a parallelcircuit consisting of the resistor R and the series circuit of variableresistor VR, and resistor R,,. Accordingly, the line 36 hassubstantially the same voltage as the positive source line 33 to keepthe transistors TR TR and TR of the switching circuits 151, 161 and 171nonconducting, deriving no bass tones.

Where, under this condition, a pedal key 11 is depressed by a playersfoot, the corresponding key switch 34 is closed to cause the voltagestored in the capacitor C, to be discharged through the resistor 11. Inthe later described length of transient time t, after key depression,the line 36 has its voltage brought to substantially the same level asthat of the negative source line 35. At this time, the transistors TR,,TR, and TR, of the keyer circuits 151, 161 and 171 are triggered to bechanged from a nonconducting to a conducting state, bringing the entirecircuitry of FIG. 2 to a stationary operating condition. Thus thefundamental bass tone signal having a predetermined pitch and theharmonic bass tone signals thereof derived from the collectors of therespective right side transistors TR TR and TR, included in the bistablemultivibrators are mixed through the corresponding diodes D, to D,, thenow triggered keyer circuits 151, 161 and 171 and the correspondingresistors R, to R,. The mixed bass tone signals are properly amplifiedby the amplifier 39 and conducted to the low pass filter 181 to form afirst composite signal. On the other hand, the harmonic bass tonesignals from the corresponding triggered keyer circuits 161 and 171 aremixed through the corresponding resistors R and R, and, after reversedin phase and properly amplified by the common emitter amplifier 191,conducted to the band pass filter 201 to form a second composite signal.The two composite signals obtained from both the filters 181 and 201 arefurther mixed together through the resistors R, and R, and properlyamplified by the amplifier 21 1.

Where, under this condition, the depressed pedal key 11 is released, thecorresponding key switch 34 is opened to have the capacitor C chargedagain with source voltage in the later described sustain time t, afterthe release. Accordingly, the entire circuitry of FIG. 2 is renderedinoperative until the pedal key 11 is depressed next time.

The curve 41 of FIG. 3 shows the operating condition of the circuitry ofFIG. 2 resulting from depression of a pedal key 11. The circuitry isbrought to a stationary operating condition in the prescribed length oftransient time t, after key depression which is defined by a timeconstant representing the product of the capacitance of the capacitor C,and the resistance of the resistor R,,. This operating condition issustained until the release of the depressed pedal key 11. Upon therelease, the circuitry of FIG. 2 is again rendered inoperable in theprescribed sustain time t determined by a time constant representing theproduct of the capacitance of the capacitor C and the compositeresistance of the parallel circuit consisting of the resistor R and theseries circuit of variable resistor VR, and resistor R The sustain timet can be freely varied within the range of t maximum and t minimum bythe adjusted sliding of the movable contact 37 of the variable resistorVR According to the circuitry of FIG. 2, the aforesaid prescribed lengthof transient time t, and the maximum and minimum sustain times t maximumand t minimum are chosen to be t, to 20 milliseconds, t maximum 1.5seconds and r minimum 0.2 second respectively.

FIG. 4 shows curves 51 and 52 showing the actually measured frequencycharacteristics of the low pass filter 181 (together with the CRcoupling network) and the band pass filter 201 of FIG. 2 according to apreferred design and a curve 53 indicating the actually measuredfrequency characteristics of mixed bass tone signals delivered from thelast output. As apparent from FIG. 4, the low pass filter 181 (togetherwith the CR coupling network) has the frequency characteristics that ithas a peak'frequency around 300 Hz and causes signals passingtherethrough to attenuate 3 dB around 150 Hz and 600 Hz. In contrast,the band pass filter 201 has the frequency characteristics that it has apeak frequency around 1,000 Hz and causes signals passing therethroughto attenuate 3 dB around 800 Hz and 1,300 I-Iz. Since the two compositesignals obtained from filters 181 and 201 are satisfactorily blendedtogether, as previously described, in reverse phase, so that themixtures are prevented from mutual complicated interference.

The bass tone produced by the mixture of the two composite signals has apeak tone pressure level around a relatively low frequency portion(around 300 Hz according to this embodiment) and also around a higherfrequency portion (around 1,000 I-Iz according to this embodiment). Thepresent inventor has experimentally found, therefore, that even where anelectronic musical instrument is played in a spacious hall, theresultant bass tones obtained by the device of this invention do notpresent a muffled sensation rich in the aforesaid low frequencycomponent as is often the case with the prior art bass tone producingdevice but bear a tone color like that of a tuba, providing a clear anddistinctive tone effect.

FIG. 5 is a schematic block circuit diagram of a bass tone producingdevice according to another embodiment of this invention.

The point at which the embodiment of FIG. 5 differs from the precedingone is that the two composite signals have different amplitudes anddifferent decaying envelopes, and that the harmonic bass tone signalsare derived in both of the opposite phases for dispensing with a phaseinverter. To this end, the circuitry of FIG. 5 causes a pair of 8' basstone signals and a pair of 4' bass tone signals to be generated in thereverse phase from the 8' tone signal source 13a and the 4 tone signalsource 14a respectively. The opposite-phase paired 8' tone signals fromthe 8' tone signal source 13a are respectively conducted to separatekeyer circuits 16a and 16a,. Similarly, the opposite-phase paired 4'tone signals from the 4 tone signal source 14a are respectively suppliedto separate keyer circuits 17a, and 17a The circuitry of FIG. 5 causesthe 8 and 4' tone signal sources 13a and 14a concurrently to act as theinverter 19, of FIG. 1, eliminating the necessity of providing aseparate inverter. The other parts of the circuitry of FIG. 5 havesubstantially the same arrangement as the corresponding parts of FIG. 1and are denoted by the corresponding numerals, description thereof beingomitted.

FIG. 6 is a concrete circuit arrangement of FIG. 5. As in FIG. 2, the16' tone signal source 12a and the 8' and 4' tone signal sources 13a and14a jointly constitute a frequency divider chain 31a consisting of threecascade connected bistable multivibrators 121a, 131a and 141a, eachincluding two transistors as TR TR TR TR and TR -TR Keyer circuits 15a,16a and 17a are constituted of emitter follower circuits 151a, 161a, and171a including transistors TR TR and TR respectively which have theirbases connected via forwardly directed diodes D D and D,;, to thecollectors of respective left or right side transistors included in thebistable multivibrators 121a, 131a and 141a, for example, the left sidetransistors TR TR and TR of each of the aforementioned three groups. Thetransistors TR to TR have the collectors directly connected to thegrounded positive source line 33 and the emitters connected viaresistors R R and R respectively, to a line 36a which is connected tothe negative power source line 35 via a capacitor C Output signalsdelivered in the later described manner from the emitters of thetransistors TR to TR are supplied to a low pass filter 181a throughcorresponding resistors R to R the coupling capacitor C an emitterfollower circuit 39a and the coupling capacitor C in turn. On the otherhand, the aforesaid keyer circuits 16a; and 1711 are comprised ofemitter follower keyer circuits l61a and 171a including transistors TRand TR which have their bases connected via forwardly connected diodes Dand D to the collectors of the right side transistors 'IR and TR of therespective groups of transistors included in the 8' and 4' tone signalsources 131a and 141a which correspond to the keyer circuits 16a and17a,. The transistors TR and TR have their collectors directly connectedto the positive power source line 33 and their emitters connected viaresistors R and R to a line 3611, which is connected via a capacitor Cto the negative power source line 35. Output signals delivered in thelater described manner from the emitters of the transistors TR and TRare supplied, as in the case of FIG. 2,'to a band pass filter 201athrough corresponding resistors R and R and the coupling capacitor CThere is further provided a trigger circuit 61 of the undermentionedarrangement so as to trigger the aforementioned keyer circuits 15a,16a,, 17a,, and upon depression of a pedal key 11. The trigger circuit61 includes a series circuit of a resistor R the normally open keyswitch 34 and a capacitor C connected across the positive and negativesource lines 33 and 35. A common connection 62 to the key switch 34 andthe capacitor C is connected to a common connection 64 to two resistorsR and R connected in series between the base of a transistor TR includedin a common emitter trigger circuit 63 and the negative source line 35.The transistor TR has its emitter connected via a resistor R to thenegative source line 35 and also via a resistor R to the positive sourceline 33. Further, the transistor TR has its collector connected via aresistor 31 to the positive source line 33 and also via a couplingcapacitor C to the input terminal 66 of a one-shot multivibrator 65which includes two transistors TR and TR and further a feedbackcapacitor C connected between the collector of the rear side transistorTR used as the output terminal 67 of the one-shot multivibrator 65 andthe base of the front side transistor TR used as the input terminal ofthe one-shot multivibrator 65. The transistor TR has its base connectedvia a resistor 32 to the positive source line 33. Both transistors TRand TR: have their collectors connected via resistors R and R to thepositive power source line 33 and also their emit ters jointly connectedto the negative source line 35.

The collector 67 of the transistor TR constituting the output terminalof the one-shot multivibrator 65 is connected to the line 360, via adiode D of the indicated polarity and a resistor R and also to the line36a, via a resistor R Between the line 36a, and the positive powersource line 33 is connected a series circuit consisting of a diode D ofthe indicated polarity, a resistor R and a variable resistor VR Thevariable resistor VR, has its movable contact 68 connected to thepositive power source line 33. There is further provided a diode D ofthe indicated polarity between a common connection 69 to the diode D andthe resistor R and a common connection 70 to the resistor R and the keyswitch 34.

The operation of a bass tone producing device arranged as describedabove according to the second embodiment will now be described byreference to FIG. 6.

While the pedal key 11 is not depressed, the corresponding key switch 34remains open and the oneshot multivibrator 65 has its front sidetransistor TR rendered conductive and its rear transistor TR renderednonconductive. Accordingly, the collector 67 of the transistor-TR hassubstantially the same voltage as that of the positive source line 33,so that the capacitor C is charged with source voltage through theseries circuit of the variable resistor VR resistor R and forwardlybiased diode D and the capacitor C is charged with source voltagethrough the series circuit of the resistors R and R In this case, thediode D is reversely biased electrically to insulate the lines 360 and36:1 from each other. Accordingly, the lines 36a and 36a havesubstantially the same voltage as the positive power source line 33,keeping nonconducting all the transistors TR to TR, included in thekeyer circuits 15a, 16a,, 17a 16a, and 17a,. As the result, there is notdelivered any bass tone.

Where, under this condition, a given pedal key 11 is depressed, thecorresponding key switch 34 is closed to cause the capacitor C to becharged with source voltage through the resistor R and also thetransistor TR of the trigger circuit 63 to have its base supplied withthe now stepped-up voltage. Since the transistor TR is brought from anonconducting to a conducting state, its output signal triggers theone-shot multivibrator 65 to reverse the condition of the transistors TRand TR included in the multivibrator 65, that is, to render the formernonconductive and the latter conductive. But after the predeterminedshort time (e.g. l ms), the

one-shot multivibrator comes back to the original state. Accordingly,the collector 67 of the transistor TR has the voltage momentarilybrought up to substantially the same level as that of the negative powersource line 35 decaying subsequently. As the result, the capacitor C hasits stored energy discharged through the resistor R the forwardly biaseddiode 16 and the energized transistor TR included in the multivibrator65 in turn. Similarly the capacitor C has its charged voltage releasedthrough the resistor R and the now energized transistor TR The lines36a, and 360 have their voltages changed from that of the positive powersource line 33 to a level substantially equal to that of the negativepower source line 35 in the later described lengths of transient timet,, and after depression of a pedal key 11, thus bringing the entirecircuitry of FIG. 6 including the keyer circuits 151a to 171a to amomentarily operating condition. Accordingly, all the transistors TR toTR included in the keyer circuits 151a to l7la are triggered to aconducting and then back to a non-conducting state. Thus the fundamentalbass tone signal having the predetermined pitch and the harmonic basstone signals thereof which are delivered from the collectors of therespective left side transistors TR TR and TR included in the bistablemultivibrators 121a, 131a and 141a are mixed through the separate keyercircuits 151a, 161a, and 171a and resistors R to R and, after properlyamplified by the amplifier 39a, supplied to the low pass filter 181a toform a first composite signal having a percussive envelope. On the otherhand, the harmonic bass tone signals which are delivered from thecollectors of the respective right side transistors TR and TR includedin the bistable multivibrators 13111 and 14la in reverse phase to thoseobtained from the collectors of the left side transistors TR and TR aremixed through the corresponding keyer circuits 161a, and 171a, andresistors R and R and conducted to the band pass filter 201a to form asecond composite signal having a percussive envelope. The two compositesignals delivered from both the filters 181a and 201a are furtherblended together through the respective resistors R and R and amplifiedby the amplifier 21 1a.

The curves 71 and 72 in FIG. 7 illustrate the rising and decayingcharacteristics of output level of the respective composite signals upondepression of the pedal key 11. As apparent from FIG. 7, the transistorTR of the trigger circuit 63 is brought from a nonconducting to aconducting state and as the result, the transistors TR and TR of theone-shot multivibrator 65 have their conditions reversed, that is, thefront side transistor TR is momentarily rendered nonconductive and therear side transistor TR conductive but subsequently both of thetransistors come back to original states. Thus the collector 67 of thetransistor TR has the voltage abruptly changed from that of the positivepower source line 33 to a level substantially equal to that of thenegative power source line 35 and gradually back to the former.According to the aforesaid discharge of the capacitor C the line 36a,has its voltage brought from that of the positive power source line 33to a level substantially equal to that of the negative power source line35- in the prescribed length of transient time t which is defined by atime constant representing the product of the capacitance of thecapacitor C and the series composite resistance of the resistor R theforwardly biased diode D and the energized transistor TR Similarlyaccording to the aforesaid discharge of the capacitor C the line 36a hasits voltage brought from that of the positive power source line 33 to alevel substantially equal to that of the negative power source line 35in the prescribed length of transient time r (in the circuitry of FIG. 6is chosen to be equal to which is defined by a time constantrepresenting the product of the capacitance of the capacitor C and theseries composite resistance of the resistor R and the energizedtransistor TR Accordingly, the entire circuitry of FIG. 6 is brought toa full operating condition quickly and then is subjected to gradualchange to non-operating state. As the collector 67 of the transistor TR:has the voltage again changed from that of the negative power sourceline 35 to a level substantially equal to that of the positive powersource line 33, the line 36a, has its voltage changed again due to theaforesaid change of the capacitor C from that of the negative powersource 35 to a level substantially equal to that of the positive powersource line 33 after the sustain time t for the first composite basstone signals composed of a 16 bass tone and an 8' and a 4' bass tone,the sustain time 1 being represented by the product of the capacitanceof the capacitor C and the internal resistances of the workingtransistors TR TR and TR and the resistors R R and R as the point 69 ismade negative through the diode D Similarly, the line 36a has itsvoltage changed from that of the negative power source line 35 to alevel substantially equal to that of the positive power source line 33after the sustain time t for the second composite bass tone signals freefrom the 16' bass tones and only consisting of the 8' and the 4' basstones, the sustain time t being represented by the product of thecapacitance of the capacitor C and the internal resistances of theworking transistors TR and TR and the resistors R, and R At this time,the entire circuitry of FIG. 6 is brought to a fully inoperable state.Upon release of a pedal key 11, the transistor TR of the trigger circuit63 is brought from a conducting to a non-conducting state but thetransistors TR, and TR, of the one-shot multivibrator 63 are notaffected at all. If the pedal key is released amidst the decayingperiod, the point 69 is released from the negative potential, and thenthe capacitor C is also charged through the diode D the resistor R andthe variable resistor VR expediting the charging operation. Thus thedecaying envelope would be changed to 71a or 71b, the slope beingcontrolled by the variable resistor VR FIGS. 8A to 8E are the frequencyspectra of the finally produced bass tone as measured at certain timeintervals. FIG. 8A shows the spectrum of the bass tone when the entirecircuitry of FIG. 6 is in a full operating condition, and FIGS. 8B to SEindicate the spectra measured about 100, 200, 300 and 400 millisecondsafter the condition of FIG. 8A.

Referring to the circuitry of FIG. 6, the low pass filter 2010 is chosento have such frequency characteristics that as shown by the curve 51a ofFIG. 9, the filter has a peak frequency of about 150 Hz and causessignals passing therethrough to attenuate 3 dB at about 80 Hz and 200Hz. This arrangement enables bass tones of lower frequency than thosepossible with the preceding embodiment to be reproduced. Obviously, thefrequency characteristics of the low pass filter 201a andband passfilter 181a may be suitably designed to meet the object and applicationsof an electronic musical instrument intended.

While the resistors R to R may also be chosen to have such resistance asconforms with the object and applications of the electronic musicalinstrument, the circuitry of FIG. 6 uses resistors having the values ofresistance indicated therein.

What is claimed is:

1. In a keyboard electronic musical instrument having pedal keys, a basstone producing device comprising:

a fundamental bass tone signal source for generating a fundamental basstone signal having predetermined pitches;

at least one harmonic bass tone signal source for generating signals ofharmonic bass tones having pitches at least one octave higher than thatof the fundamental bass tone represented by the signal generated by saidfundamental bass tone signal source;

normally nonconductive keyer circuits rendered conductive upon thedepression of an associated one of said pedal keys to derivetherethrough the respective bass tone signals from both said bass tonesignal sources;

signal composing means for mixing in a preset ratio both the bass tonesignals obtained through said individual keyer circuits;

a first tone coloring filter supplied with output mixed signals fromsaid signal composing means having a relatively low peak frequency toform a first composite signal;

a second tone coloring filter supplied with the harmonic bass tonesignal obtained through the corresponding one of said keyer circuits andhaving a peak frequency higher than that of said first tone coloringfilter to form a second composite signal;

means for reversing the phase of said harmonic bass tone signal in saidsecond composite signal relative to the phase of said harmonic bass tonesignal in said first composite signal; and

a final signal composing means for mixing the first and second compositesignals in a predetermined ratio.

2. A bass tone producing device according to claim 1 wherein saidharmonic bass tone signal source comprises two units for generatingdifferent harmonic bass tone signals, and there is further providedanother signal composing means for mixing in a preset ratio two outputsignals from both said harmonic bass tone signal source units.

3. A bass tone producing device according to claim 1 wherein saidfundamental and harmonic bass tone signal sources comprise a frequencydivider chain comprised of a plurality of cascade-connected bistablemultivibrators each including two transistors, and said keyer circuitscomprise emitter follower circuits each including a transistor which hasits base connected via a diode to the collector of one of the twotransistors included in the corresponding one of said bistablemultivibrators and its emitter connected via a resistor to a line whichis connected to one of a pair of positive and negative power sources viaa resistor and a normally open switch closed upon depression of acorresponding key on said pedal keyboard, said transistor having itscollector connected to the other power source with a resistor networkconnected between the collector and emitter of said transistor.

4. A bass tone producing device according to claim 1 further including atrigger circuit wherein said fundamental and harmonic bass tone signalsources comprise a frequency divider chain comprised of a plurality ofcascade-connected bistable multivibrators each including twotransistors, and said keyer circuits comprise a first group of emitterfollower circuits each including a transistor which has its baseconnected via a diode to the collector of one of the two transistorsincluded in the corresponding one of said bistable multivibrators andits emitter connected via a resistor to a line which is connected via acapacitor to one of a pair of positive and negative power sources, saidtransistor having its collector connected to the other power source andsaid line being connected via a resistor and a diode to the outputterminal of said trigger circuit rendered conductive upon depression ofone of said pedal keys and also connected via a series circuit of adiode and a resistor network to the other power source; and a secondgroup of emitter follower circuits each including a transistor which hasits base connected via a diode to the collector of the other transistorincluded in the corresponding one of said bistable multivibrators andits emitter connected via a resistor to another line which is connectedvia a capacitor to said one power source, said transistor having itscollector connected to the other power source line and said line beingconnected via a resistor to the output terminal of said trigger circuitand also connected via a resistor network to the other power source.

5. A bass tone producing device according to claim 1 wherein said firsttone coloring filter is a low pass filter.

6. A bass tone producing device according to claim 1 wherein said secondtone coloring filter is a band pass filter.

7. A bass tone producing device according to claim 1 wherein said firstsignal composing means comprises a plurality of resistors connected atone end to the corresponding output terminals of said keyer circuits,said resistors being jointly connected at the other ends thereof.

8. A bass tone producing device according to claim 1 wherein said finalsignal composing means comprises two resistors connected at one end tothe corresponding tone coloring filters, said resistors being jointlyconnected at the other ends thereof.

9. A bass tone producing device according to claim 4 wherein saidtrigger circuit includes a one-shot multivibrator.

10. A bass tone producing device according to claim 1 wherein said meansfor reversing the phase of said harmonic bass tone signal in said secondcomposite signal comprises a phase inverter coupling the harmonic basstone signal from said keyer circuits to said second tone coloringfilter.

11. A bass tone producing device according to claim 1 wherein saidmeansfor reversin the phase of said harmonic bass tone signal in saidsecond composite signal comprises means in said harmonic bass tonesignal source for generating pairs of opposite phase harmonic bass tonesignals, one of said bass tone signals being coupled to said first tonecoloring filter, and the other of said bass tone signals, which is outof phase with respectto said one of said bass tone signals, beingcoupled to said second tone coloring filter.

1. In a keyboard electronic musical instrument having pedal keys, a basstone producing device comprising: a fundamental bass tone signal sourcefor generating a fundamental bass tone signal having predeterminedpitches; at least one harmonic bass tone signal source for generatingsignals of harmonic bass tones having pitches at least one octave higherthan that of the fundamental bass tone represented by the signalgenerated by said fundamental bass tone signal source; normallynonconductive keyer circuits rendered conductive upon the depression ofan associated one of said pedal keys to derive therethrough therespective bass tone signals from both said bass tone signal sources;signal composing means for mixing in a preset ratio both the bass tonesignals obtained through said individual keyer circuits; a first tonecoloring filter supplied with output mixed signals from said signalcomposing means having a relatively low peak frequency to form a firstcomposite signal; a second tone coloring filter supplied with theharmonic bass tone signal obtained through the corresponding one of saidkeyer circuits and having a peak frequency higher than that of saidfirst tone coloring filter to form a second composite signal; means forreversing the phase of said harmonic bass tone signal in said secondcomposite signal relative to the phase of said harmonic bass tone signalin said first composite signal; and a final signal composing means formixing the first and second composite signals in a predetermined ratio.2. A bass tone producing device according to claim 1 wherein saidharmonic bass tone signal source comprises two units for generatingdifferent harmonic bass tone signals, and there is further providedanother signal composing means for mixing in a preset ratio two outputsignals from both said harmonic bass tone signal source units.
 3. A basstone producing device according to claim 1 wherein said fundamental andharmonic bass tone signal sources comprise a frequency divider chaincomprised of a plurality of cascade-connected bistable multivibratorseach including two transistors, and said keyer circuits comprise emitterfollower circuits each including a transistor which has its baseconnected via a diode to the collector of one of the two transistorsincluded in the corresponding one of said bistable multivibrators andits emitter connected via a resistor to a line which is connected to oneof a pair of positive and negative power sources via a resistor and anormally open switch closed upon depression of a corresponding key onsaid pedal keyboard, said transistor having its collector connected tothe other power source with a resistor network connected between thecollector and emitter of said transistor.
 4. A bass tone producingdevice according to claim 1 further including a trigger circuit whereinsaid fundamental and harmonic bass tone signal sources comprise afrequency divider chain comprised of a plurality of cascade-connectedbistable multivibrators each including two transistors, and said keyercircuits comprise a first group of emitter follower circuits eachincluding a transistor which has its base connected via a diode to thecollector of one of the two transistors included in the correspondingone of said bistable multivibrators and its emitter connected via aresistor to a Line which is connected via a capacitor to one of a pairof positive and negative power sources, said transistor having itscollector connected to the other power source and said line beingconnected via a resistor and a diode to the output terminal of saidtrigger circuit rendered conductive upon depression of one of said pedalkeys and also connected via a series circuit of a diode and a resistornetwork to the other power source; and a second group of emitterfollower circuits each including a transistor which has its baseconnected via a diode to the collector of the other transistor includedin the corresponding one of said bistable multivibrators and its emitterconnected via a resistor to another line which is connected via acapacitor to said one power source, said transistor having its collectorconnected to the other power source line and said line being connectedvia a resistor to the output terminal of said trigger circuit and alsoconnected via a resistor network to the other power source.
 5. A basstone producing device according to claim 1 wherein said first tonecoloring filter is a low pass filter.
 6. A bass tone producing deviceaccording to claim 1 wherein said second tone coloring filter is a bandpass filter.
 7. A bass tone producing device according to claim 1wherein said first signal composing means comprises a plurality ofresistors connected at one end to the corresponding output terminals ofsaid keyer circuits, said resistors being jointly connected at the otherends thereof.
 8. A bass tone producing device according to claim 1wherein said final signal composing means comprises two resistorsconnected at one end to the corresponding tone coloring filters, saidresistors being jointly connected at the other ends thereof.
 9. A basstone producing device according to claim 4 wherein said trigger circuitincludes a one-shot multivibrator.
 10. A bass tone producing deviceaccording to claim 1 wherein said means for reversing the phase of saidharmonic bass tone signal in said second composite signal comprises aphase inverter coupling the harmonic bass tone signal from said keyercircuits to said second tone coloring filter.
 11. A bass tone producingdevice according to claim 1 wherein said means for reversing the phaseof said harmonic bass tone signal in said second composite signalcomprises means in said harmonic bass tone signal source for generatingpairs of opposite phase harmonic bass tone signals, one of said basstone signals being coupled to said first tone coloring filter, and theother of said bass tone signals, which is out of phase with respect tosaid one of said bass tone signals, being coupled to said second tonecoloring filter.